The quoted resolution of Polaroid Type 55 of 160-180 line pairs/mm (negative) probably indicates an emulsion optimised for this purpose. The relatively poor print sharpness of 20-25 line pairs/mm is caused by sideways image spread during diffusion (a thin layer of developer separates the negative and print, which are not in perfect contact). The spectral sensitivity may reflect the fact that Polaroid Type 55 was introduced in 1961 and has probably remained exactly the same ever since. Polaroids first panchromatic film came out in 1955, so their knowledge of dye sensitization in 1961 may not have been cutting edge. The relatively low negative Dmax may reflect the migration of silver to the print.
I only ever used Type 665 (the smaller pack film size) a few times, because of the cost, and because the one stop difference between a satisfactory negative and print seemed annoying. I cynically wondered why Polaroid hadnt re-developed Type 55 to remove this discrepancy. However, Land published a graph of an early trial with a five stop difference, so it was probably an extraordinary accomplishment to get the difference down to only one stop. (The white powder from a spilled sodium sulfite solution in the car was a further annoyance, which encouraged me only ever to take water into the field, and leave full clearing until I got home).
I suspect most Type 55 is exposed for the negative, and as previously suggested it would be far easier to work out a portable monobath process for a specific commercially manufactured black and white film, rather than attempt to re-engineer an exact replica of Type 55. Conventional cameras could then continue to be used, and there would be no need to emulate Polaroid pack film manufacture.
The Kodak Bimat web processing process, which was intended for conventional negative materials, is worth considering in this context (see Grant Haist,
Modern Photographic Processing, New York: Wiley, 1979, vol. 2, pp. 397-399). Basically, a strip of photographic film base was coated with a polymer or gelatin layer presoaked with a special monobath processing solution. This moist film was then brought into contact with conventionally exposed film. Negative development was complete in one minute, though four minutes were required to transfer a positive to the web film. Although the results were relatively stable, additional fixation and washing may have been required within ten days for archival permanence. Kodak originally developed Bimat for Cold War military reconnaissance applications in about 1960 (Tregillus et al. US patent 3179517), and it was later declassified and used in the unmanned Lunar Orbiter photographic missions which surveyed the moon for landing sites (see
http://www.lpi.usra.edu/resources/lunar_orbiter/book/introduction.shtml).
Haist cites the following formula (from Tregillus) as useful for imbibing into the absorbent layer of the web:
2,2-Iminodiethanol-sulfur dioxide
addition compound (20 mole percent S02) 190.0 g
Hydroquinone 11.6 g
4,4-Dimethyl-l-phenyl-3-pyrazolidone 1.0 g
Sodium thiosulfate, desiccated 5.4 g
Potassium iodide 0.42 g
Water to make 1.0 liter
The second developing agent appears to be a phenidone, probably dimezone-S. The amine-sulfur dioxide addition product serves as both an alkali and as a preservative. Perhaps triethanolamine (TEA) or a more conventional preservative-alkali system could be substituted. There may have been additional physical development nuclei added to the receiver for the positive image. The principle behind diffusion transfer resembles reversal processing in that there is both a positive and negative present in the developed silver halide emulsion layer; it is the unexposed silver halides (representing the positive image) that are dissolved and transferred to the image-receiving light-insensitive second support.
In his chapter on monobaths, Haist (p. 187) cites an apparently related formula for a thickened monobath (US Patent 3,392,019, by John C. Barnes and Gerald J. Johnston of Kodak):
Methylaminoethanol-sulfur dioxide
addition product (17.8 SO2) 75.0 g
l-Phenyl-4,4-dimethyl-3-pyrazolidone 2.0 g
Hydroquinone 10.0 g
Sodium thiosulphate crystals (5 H20) 50.0 g
Potassium iodide 0.5 g
pH 10.5
Water to make 1.0 liter
Colloidal silver (Carey Lea Silver) 0.2 g
Natrosol (hydroxyethycellulose) 0.2 g
(Hercules, Inc.)
The colloidal silver provides physical development nuclei, allowing a lower thiosulphate concentration, and prevents excessive fog. Unfortunately the colloidal silver and amine product put this formula out of standard home developer mix capabilities, although somebody may be able to suggest a relatively straightforward method of preparing the required amount of colloidal silver from a silver nitrate solution. The thickening agent can be a water soluble polymer or gum, methylcellulose, silica gel, starch, etc.
Processing involved applying this thickened solution to the surface of an emulsion. It was allowed to stand for 10 min at 70 degrees F before being rinsed away to exhibit a very high quality, completely developed and fixed image. Photographic speed, contrast, granularity, and acutance were said to be equal to those produced when the film was developed in the normal way in D-76, followed by separate fixation. Imagine a pod in special film envelope, or squeezing a bead of this stuff out of a tube (a new product line for Photographers Formulary?), rolling it over sheet film (or a short length of roll film), and then rinsing it off. Monobaths require much less washing than conventional fixation, but an additional processing step might be required to get rid of the antihalation backing.
For prints, perhaps it might be more appropriate to revive a basic diffusion transfer process. Image transfer is popular with Polaroid colour materials, but apparently does not work with the current Polaroid black and white products. In this case, it may be worth trying an alternative procedure with other black and white emulsions. Edwin H. Land, in his paper The Universe of One-Step Photography in
Pioneers of Photography: Their Achievements in Science and Technology, edited by Eugene Ostroff (Springfield, Va.: SPSE, The Society for Imaging Science and Technology, 1987, pp. 219-248), describes and reproduces some of his first experiments carried out in March 1944:
The film was Kodak Contrast Process Ortho. The developer was D-8 with some hypo added to it. The esoteric material used for image-receiving was either a sheet of blotting paper or a sheet of filter paper. Nothing was done to it beforehand. It was wet with developer. Next we put this wet sheet of filter paper down on a Plexiglas sheet, took the film, which had been exposed in the camera, rolled it against the filter paper, and left it there for about a minute. At the end of the minute we peeled it off, and what we had was a negative and a black-and-white positive image on the filter paper (p.219)
Plate 1a, p.233, reproduces one of these images deposited in alpha-cellulose, which doesnt look too bad, except for a few flecks of coarse paper grain. Plate 1b, a more conventional looking glossy image, was produced on opal acetate, with the surface hydrolysed to regenerate it to cellulose. Both of these were subsequently washed. Plate 1c is a transfer to a negative emulsion which had been fixed out, leaving silver nuclei as very fine particles within the gelatin. This image is a strong sepia color. Although Land subsequently went to a lot of trouble to get neutral toned images, sepia is now perfectly acceptable again, and if you relax Lands requirement that the prints be dry and archival as soon as they come out of the camera, home brew Polaroid might be practicable.
My initial attempt, following these sketchy instructions, using a roller, some cheap cartridge paper, lith film, D-8 and increasing amounts of hypo, failed. I wondered if the amount of sodium thiosulfate required is a critical factor, and for my second attempt I re-started with the following formula from Lands US patent 2,543,181:
Sodium sulfite (anhydrous) 9 g
Hydroquinone 4.5 g
Sodium hydroxide 3.75 g
Potassium bromide 3 g
Sodium thiosulfate 10 g
Water to make 170 cc
This is very roughly equivalent to D-8 diluted 1 + 1 with about 60 g/litre sodium thiosulfate. I reduced the quantities to 100 ml which was sufficient for 4 x 5 inch paper in a small flat bottomed tray.
Once again I still couldnt get anything but smudges on ordinary paper, but I was able to get brown positive images on fixed-out photographic paper. The paper was soaked in the developer, placed in a large empty flat bottomed plastic container. A sheet of exposed film was slapped onto it and left for a minute or two. Kodak Professional Copy and Tri-X Ortho didnt seem to work as well as the generic lith film, so I didnt persist with them (I suspect they may require significantly different exposure and development times). I havent tried photographic paper as the negative material. They may work, but I suspect it may be easier to mobilise the silver in lith film. The amount of hypo in the developer is not sufficient to fix the film to completion (as in a monobath), so if you want to try and salvage or inspect the negative you need to separately fix it. The print seems to need at least a water rinse to get some of the highly alkaline developer off it. The colloidal silver particles that make up the image are very delicate and can be easily wiped off, so handle with care. Fixer may also be advisable to neutralise the developer and better stabilise the print. According to Haist, the main neutralising chemical in Polaroid coater swabs is ammonia, but Id rather not have a an open tray of it in the darkroom.
For my next batch of developer, I added 5ml of glycerol/glycerin to 100ml of developer in an attempt to improve the contact between the developer and the positive. However this didnt work at all, presumably because the quantity was too great to ensure satisfactory contact for diffusion. Subsequent investigation suggests there is nothing inherently wrong with glycerin in the right quantity: United States Patent 3645731 (Agfa-Gevaert researchers, 1970) claims increased stability of diffusion transfer activator baths with trisodium phosphate and polyalcohols (glycerol being particularly suitable) in quantities preferably between 15 and 30 ml. per liter.
In my next session I had trouble getting the exposure and development right. The Image color was relatively neutral to start with, but then went reddish once I added a drop of glycerin. This may have coincided with exhaustion of the hydroquinone (see attached image; in some cases I held detail in the white dress but the doll's face seemed to be solarised).
Incidentally, Land seems to have experimented with some very exotic developers for his pods. It didnt matter to him that these developing agents oxidised rapidly, as the pod excluded air until it was broken for processing, and then the developer was rapidly spread between the negative and the print, before the air could have much effect. One of his patents mentions mixing these developers in a nitrogen atmosphere, which raises questions regarding manufacturing costs and practicality.
The receiving paper doesnt necessarily have to be fixed out photographic paper or film. Land discusses sodium sulphide and heavy metal salts like lead as silver precipitating nuclei on the receiving sheet, but colloidal silver may be preferable in the home darkroom. I havent found a clear, simple and practical description of Carey Leas dextrin method of preparing colloidal silver, in which a solution of silver nitrate is gradually added to a solution of sodium hydroxide and starch. The precipitate is then allowed to settle, and the liquid poured off, possibly after alcohol is added. If you could calculate the right quantities, you might to be able to mix a stock solution which could go directly into the Barnes and Johnston thickened monobath formula above, or a 1% gelatin solution for coating on paper. Example 1 in US patent 4888267 gives a similar but far more complex procedure, with completely unrealistic quantities.
My first attempt to make an alternative form of colloidal silver was a failure. Following B.H. Carroll et al.s The Photographic Emulsion (1968), p. 142: Colloidal silver sulphide was prepared by adding first 2.34. ml of 0.107 M Na2S2O3 [i.e. 24.8 g/litre sodium thiosulfate], then 5.0 ml of 0.100 M AgN03 [i.e. 17 g/litre silver nitrate] to 170 ml of warm 1 per cent gelatin solution; the mixture was allowed to stand about an hour before use to complete the decomposition of the silver thiosulphate. I made a mistake scaling the quantities and the colloidal silver/gelatin coating is too dark on the paper. On soaking in developer, the emulsion seems to be stable, although it immediately fogged exposed film. Perhaps the correct quantities may well work, although I might give it a rest for awhile.
Perhaps this long message might encourage other experimenters to explore some of the possibilities, hopefully without necessarily having to prepare your own film from scratch yet. However preparing your own emulsion could be an advantage as you could control silver content and hardening, pick your own image size, and use a paper base rather than glass, acetate or polyester. Or maybe you could make silver gelatin ambrotypes on black anodized aluminium, develop them in a monobath paste in your dark tent, and be a step ahead of the wet plate crowd!
And Ansel's gonna be pissed. I think he's going to place them on zone 20 or so.
). There are also some developers and silver halide solvents. The film sheet is a film sheet but the reciever sheet is a special thing which forms the positive print. The whole thing is like a monobath.
